Method for predicting failure of geotechnical structures

Abstract

Provided is a method of predicting failure in geotechnical structures using an AE method instead of a conventional displacement or stress measuring method, which belongs to a field of rock mechanics and geotechnical engineering. The method is a measurement technology for identifying signs of failure in geotechnical structures using Acoustic Emission (AE) signals generated by damage in the geotechnical structure and also providing management standard for failure prediction.

1. A method of predicting failure in geotechnical structures, comprising:
 measuring specific AE signals generated from damages to an outer waveguide by a deformation or movement in the geotechnical structures using a measurement apparatus affixed with AE sensors, wherein the measurement apparatus affixed with AE sensors is fixedly installed in a borehole and passes through an expected failure plane and includes both an inner waveguide, which is formed of metallic material that is intended to prevent sharp attenuations of AE signals, and an outer waveguide; two AE sensors are attached to the inner waveguide so that the expected failure plane is interposed between two AE sensors, and one of which above the other; the outer waveguide firmly encloses at least one AE sensor as well as the inner waveguide; and the outer waveguide is formed of a homogeneous brittle material that is intended to generate specific AE signals regardless of ground conditions or formations when the outer waveguide is damaged by the events that indicated there are deformations or movements in the geotechnical structures; 
 obtaining arrival times from an AE signal generated from the damages to the outer waveguide by a specific event, wherein the AE signal is measured by the upper AE sensor and the lower AE sensor and the arrival time is defined as time when an initial AE signal waveform arrives at each of the upper and lower AE sensors; 
 determining a distance between the upper AE sensor and a source of the AE signal or a distance between the lower AE sensor and the source of the AE signal from a difference between the arrival times obtained from the AE signal measured by the upper AE sensor and the lower AE sensor; 
 obtaining at least one parametric values of a summed magnitude value, an accumulated summed magnitude value and summed magnitude frequency value of the AE signals measured by the upper or lower AE sensor, in order to predict the failure in the geotechnical structures from the AE signals measured by the upper or lower AE sensor; 
 performing at least one of laboratory tensile, shear and compression tests with respect to a laboratory testing measurement apparatus affixed with AE sensors that is the same as the installed measurement apparatus in the geotechnical structures, and obtaining AE signals generated by the damage of an outer waveguide of the laboratory testing measurement apparatus affixed with AE sensors, wherein obtaining laboratory parametric values with applied load in the laboratory tests, which correspond to the parametric values in the geotechnical structures, are extracted from AE signals generated by the damage of the outer waveguide of the laboratory testing measurement apparatus; and 
 comparing one or more reference parametric values and obtained parametric values in geotechnical structures, wherein the one or more reference parametric values indicate the damage levels in geotechnical structures, are among laboratory parametric values corresponding to the parametric values in the geotechnical structures and the obtained parametric values in geotechnical sturctures are obtained in the parametric values-obtaining step in geotechnical structures, and 
 wherein the summed magnitude is a parameter which is indicated by G(d)ΘF(E) of the AE signals and the AE signals are measured during a desired time interval Δt 1  and generated from the damage to an outer waveguide by the specific events, 
 and the accumulated summed magnitude is a parameter, which is an accumulative sum of the summed magnitude values with respect to the different specific events according to the lapse of time, and 
 the summed magnitude frequency is a parameter which is a total of the summed magnitude values obtained during a desired time interval Δt 2  with respect to the different specific events according to the lapse of time, and 
 assuming that k is a natural number equal to or larger than 2, Δt 2  is Δt 2 =kΔt 2 , and 
 d is a distance between one of the upper and lower AE sensors and the source of the AE signal, which is used in obtaining the summed magnitude value in the determining of distance from specific source and 
 G(d) is an attenuating function according to d, and is indicated by G(d)=A 1 d+A 2  or G(d)=B 1 e −d +B 2 , and 
 A 1 , A 2 , B 1  and B 2  are regression coefficients which are decided by a material of the inner guide, and 
 Θ is an operator decided by G(d), and 
 F(E) is an energy function of the AE signal used in obtaining of the summed magnitude value. 
 
     
     
       2. The method of  claim 1 , wherein F(E) is one of 
       
         
           
             
               
                 log 
                 ⁡ 
                 
                   ( 
                   
                     ppA 
                     
                       2 
                       ⁢ 
                       π 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       f 
                     
                   
                   ) 
                 
               
               , 
               
                 
                   log 
                   ( 
                   
                     
                       
                         
                           ∑ 
                           
                             j 
                             = 
                             1 
                           
                           n 
                         
                         ⁢ 
                         
                           A 
                           j 
                           2 
                         
                       
                       
                         n 
                         ⁢ 
                         
                             
                         
                       
                     
                   
                   ) 
                 
                 ⁢ 
                 and 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   dB 
                   peak 
                 
               
               , 
             
           
         
         wherein ppA is a maximum particle acceleration of the AE signal used in obtaining the summed magnitude value, 
         f is a dominant frequency of the AE signal used in obtaining the summed magnitude value, 
         n is a count of the AE signal used in obtaining the summed magnitude value, 
         A j  is an amplitude of a j-th waveform forming the AE signal used in obtaining the summed magnitude value, which is over a threshold value, and 
         dB peak  is a maximum amplitude in the waveform forming the AE signal used in obtaining the summed magnitude value. 
       
     
     
       3. The method of  claims 1  or  2 , wherein coefficients of reference parameters corresponding to the damage levels in the geotechnical structures are C 1 , C 2  and C 3 , and,
 the reference coefficient C 1 ,which is the parameter value, is a value when force corresponding to 80% of failure strength is exerted to the laboratory testing measurement apparatus affixed with AE sensors used in the laboratory test, 
 the reference coefficient C 2 , which is the parameter value, is a value when force corresponding to 60% of failure strength is exerted to the laboratory measurement apparatus affixed with AE sensors used in the laboratory test, and 
 the reference coefficient C 3 , which is the parameter value, is a value when force corresponding to 40% of failure strength is exerted to the laboratory measurement apparatus affixed with AE sensors used in the laboratory test.